Inductors are used in many integrated circuits and other semiconductor devices and particularly in radio frequency (RF) circuits. It can be useful for the inductors to have high inductance values. This is difficult to achieve, however, on integrated circuits and other semiconductor devices because high inductance is achieved using larger inductors which are formed at the expense of other device features.
Inductors are used to form various transformer devices and an inductor is generally characterized as a coil of wires or a winding circuit. A transformer is generally formed of two or more such inductor coils. One inductor coil through which an electric current is flowing, can produce a magnetic field and a changing magnetic field within an inductor coil induces a voltage across the ends of the coil via electromagnetic induction. A transformer is a static electrical device that transfers energy by inductive coupling between its winding circuits. A varying current in the primary winding, i.e. inductor coil, creates a varying magnetic flux in the transformer's core and thus a varying magnetic flux through the secondary winding, i.e. inductor coil. The varying magnetic flux induces a varying electromotive force or voltage in the secondary inductor coil. When multiple inductor coils are used, multiple transformer devices are formed.
To improve the inductance of inductors, three-dimensional inductors were developed wherein the inductor is formed using a plurality of metal layers to form a helical shape. The portions of the metal from the different metal levels are interconnected to form an inductor. For a greater inductance to be achieved, however, a greater number of metal layers is used.